In a modern computed tomography system, a direct conversion X-ray detector based on cadmium telluride or cadmium zinc telluride is in particular used for photon-counting applications. After being taken into operation such a detector exhibits a counting rate drift which can result in artifacts during the imaging process. In order to achieve a reliable, high-resolution and interference-free image generation it is necessary for the cadmium telluride or the cadmium zinc telluride to have reached a stable state of equilibrium in respect of an occupation of impurities following the operation of turning on the computed tomography system.
Such a state of equilibrium of the impurity occupation is dependent in this situation on the voltage present at the X-ray detector. The attainment of a state of equilibrium adequate for artifact-free image generation after switching on a high voltage at the X-ray detector is a process which can extend over a period of several hours. With regard to use in day-to-day medical practice it is desirable for reasons of efficiency for the computed tomography system to be available ready for operation on as permanent a basis as possible. On the other hand, the extended period of time required to reach the state of equilibrium would result in a considerable loss of time for examinations in the event of a daily power-up procedure in practical operation. One could therefore be inclined to consider running the power supply of the X-ray detector continuously.
An X-ray detector is arranged on the rotating assembly of the computed tomography system together with a plurality of other consumer loads, for example the X-ray tube, image-processing electronics components as well as coolers and fans. Said consumer loads, with the exception of the anode voltage of the X-ray tube, constitute a continuously operated basic load of several kW. On account of said basic load, uninterrupted operation of the rotating assembly, in other words including nights and weekends, in order to maintain the state of equilibrium in the X-ray detector would be inefficient in terms of energy use.
As a possible way of avoiding this, the primary power supply to the consumer loads on the rotating assembly could be configured in such a manner as to have two switching or operating states, where in primary operation all the consumer loads and in ancillary operation only the X-ray detector are/is supplied with power. Such a procedure would however require that the power distributor of the rotating assembly would need to be designed with intelligence for switching off individual consumer loads, and would in this case itself need to undertake to differentiate the two operating states in a control electronics unit specially designed for the purpose because all the other electronics components would be switched off in ancillary operation.
The control electronics unit would for its part need to be incorporated into the communication between the other electronics components, in which case it would be necessary to consider that on the transition from ancillary to primary operation the remaining components first undergo their system startup before they have a full communications capability, in other words signal errors could occur while the control electronics unit of the power supply is already in operation. Such a solution by way of a division of the primary power supply would thus be susceptible to faults, which not least against the background of the high requirements for particularly stable operation in the medical sector, which are also reflected in approval procedures, results in such a solution variant being discarded.